There are numerous types of vertically raisable flexible curtain doors. All of these types of door share the common feature of a flexible curtain, e.g. made of plastic-impregnated cloth, two vertical guiding slideways on either side of the door, and an actuator system. They differ essentially in the ways they operate and in the widths of their side guideways, which are generally constituted by channel section bar.
In a first type of door, the flexible curtain is designed to be raised by being wound around a motor-driven shaft extending over the door. While it is being raised, the curtain remains in a single vertical plane and as a result the side guideways holding it are narrow in width.
In a second type of door, the flexible curtain is designed to be raised by being wound around a bar fixed to its bottom edge. Two straps (at least) are looped around the curtain with each strap having one end fixed to a fixed point situated at the level of the door's lintel, and having its other end fixed to a shaft extending over the door, with said shaft being rotated by a motor. As they are wound round the shaft, the straps cause the curtain to be wound around the bar, thereby raising the curtain. Since the diameter of the roll of curtain increases during curtain-raising, the side guideways must be at least as wide as the diameter of the fully-wound curtain.
In a third type of door, the flexible curtain is designed to be raised by being folded, concertina-like. It comprises a plurality of regularly spaced-apart horizontal hinge bars which are connected to loops through which vertical straps are passed with one end of each strap being fixed to the bottom hinge bar and with the other end being fixed to a motor-driven shaft extending over the door. Since the curtain forms a bundle of increasing volume while the door is being opened, the width of the side guideways is not less than the width of the curtain when completely folded.
In all of these three types of door, the flexible curtain has a bar fixed to its bottom edge. A concertina-type door must include, and the other two types of door may include, additional horizontal reinforcing bars which are regularly spaced apart and which are intended to stiffen the curtain. These reinforcing bars are generally slid into sheaths provided on one of the faces of the curtain and they are essential for curtains giving access to the outside and therefore exposed to the wind. This is particularly true of quick-acting doors sometimes referred to as "goods-handling" doors giving access to warehouses and similar storage premises.
There are several different ways in which the flexible curtain fitted with its bar(s) may be positioned relative to the channel section side guideways, regardless of guideway width: firstly the side edges of the flexible curtain itself may be received or may not be received in the guideways; secondly, apart from the bottom bar which is always received therein, other reinforcing bars (which constitute hinges or concertina-type doors) may or may not be received therein, or only some of them may be so received.
In any event, the bottom bar and optionally such reinforcing bars as are also received in the guideways, serve(s) to prevent the curtain from escaping from the plane of the door when subjected to thrust. Although this way of using bars is desirable and even sought-after when the curtain is subjected to a thrust which is uniformly distributed over its area (e.g. wind), it is, on the contrary, detrimental when the curtain is subjected to a violent thrust exerted on a small area. The above-mentioned goods-handling doors which are opened and closed several tens of a times a day to allow goods-handling and/or transportation vehicles to pass through are particularly exposed to thrust of this type. For example, when a vehicle backs into a curtain stiffened by reinforcing bars which are received in the side risers, the curtain is prevented from escaping from the plane of the door and it often happens that the curtain is torn and some of the bars are irreversibly deformed. The door is then no longer operable, at least for as long as it takes for the deformed bars to be replaced. The traffic between the inside and the outside which would normally pass through the door is interrupted for the time being, such that in addition to the cost of repairing the damaged door, there is also the cost of lost business.
The present invention seeks to remedy these drawbacks by providing a reinforcing and guiding bar for a flexible curtain in a vertically raisable door where the bar allows the curtain to escape from the side guideways when subjected to a given amount of thrust.